A Front-row Seat At The Rock Show

SCIENCE & MEDICINE

A Series Of Spacecraft To Get Closer To Comets

August 25, 2002|By Robert S. Boyd, Knight Ridder Newspapers

WASHINGTON -- For millions of years, comets have been swooping past Earth and occasionally bashing into us. Now Earthlings are turning the tables on those luminous, mysterious, potentially dangerous visitors from outer space.

No less than four spaceships are currently on their way -- or soon will be -- to five or six nearby comets.

Starting next January, they will take closeup pictures, collect samples, punch a hole and even land on the surface of their assigned targets.

"This is a golden decade for cometary science," said Donald Yeomans, who tracks comets and asteroids at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

Comets are chunks of rock and ice surrounded by glowing clouds of gas and dust that come from the outer edge of the solar system. Asteroids are fragments of rocks or metal that orbit the sun, largely between Jupiter and Mars.

Two NASA comet missions, Stardust and Contour, already have been launched. A European spaceship, Rosetta, will follow in January, and a third American project, Deep Impact, a year later.

There is the possibility that one project has suffered a setback, though. On Aug. 15, NASA announced that it had lost contact with Contour 140 miles above the Indian Ocean. The spacecraft was supposed to leave Earth's orbit early in the morning. By afternoon, antennas around the world had not received a signal from Contour. The space agency was checking along the craft's intended path in hopes of locating it.

"We really are still in a search mode, trying to communicate with the spacecraft," National Aeronautics and Space Administration spokesman Don Savage said this past week.

Why this sudden surge of scientific interest in comets, which have intrigued and sometimes terrified human beings in the past?

One reason, Yeomans pointed out, is home-planet security.

We live in a veritable shooting gallery of comets and asteroids that periodically pummel the Earth, such as the object that hastened the death of the dinosaurs 65 million years ago.

"These things can run into us," Yeomans said. "If one of them has our name on it, we've got to know what they're made of."

Such information could be crucial for any attempt to deflect a comet or asteroid from colliding with Earth.

Basic scientific curiosity is also driving the comet hunt, especially now that modern technology makes it possible to visit comets efficiently and relatively cheaply.

The four missions will cost between $150 million and $325 million apiece -- peanuts for space projects. Contour, for example, is budgeted at $159 million, compared to $1.5 billion for a major planetary explorer like Galileo.

"There's an awful lot of high-class science waiting to be done," said Tom Morgan, who directs the three U.S. comet hunts from NASA headquarters in Washington.

According to Joseph Veverka, an astronomer at Cornell University in Ithaca, N.Y., and chief scientist for the Contour mission, comets are among solar system's biggest mysteries. "We really have more ideas about comets than facts," he said.

A trillion or more of these ghostly objects are believed to hang out in the deep cold beyond the fringes of the solar system. Periodically, gravity nudges one of them into a long looping voyage past the planets and around the sun.

Because they are so far away, comets are believed to preserve the original gas and dust left over from the formation of the solar system 4.5 billion years ago.

Astronomers regard them as virtual time machines that enable them to study the raw materials of our sun, planets and moons.

"They are truly the building blocks of the solar system," Morgan said.

Furthermore, scientists believe comets brought huge quantities of water and carbon-based molecules to Earth during the era of heavy bombardment, when our planet was young.

"These missions will help us understand where our oceans came from," Morgan said.

Some theorists speculate that the cometary molecules may even explain how life got started on Earth. "We may really be the progeny of comets," Veverka wrote in the journal Science last month.

Each of the current fleet of comet hunters has a different goal.

Among them:

Stardust, launched in February 1999, will be the first spaceship to bring a sample of a comet back to Earth. It is due to reach Comet Wild-2 in January 2004, flying through a cloud of dust and debris that forms the glowing head, or coma, of the comet.

A dust-catcher, shaped like a large tennis racket filled with an almost invisible foam called aerogel, will trap particles of the coma and tuck them away in a clamshell-like return capsule. The package is supposed to parachute gently down on the Utah desert in January 2006, for earthbound scientists to analyze.

Contour (for Comet Nucleus Tour), launched on July 3, is scheduled to visit two, possibly three, comets to study the differences between their rocky cores, which are hidden from earthly telescopes by their veils of dust.